The ENQUIRER’s sneak peek at shocking tell-all!

Paul Newman‘s grieving widow Joanne Woodward will be shattered by the publication of a tell-all book about her beloved husband – exposing his long-ago extramarital affair.

Often lauded as Hollywood’s most solid marriage, the Newmans’ 50-year union stood out as a Rock of Gibraltar in a town of quickie marriages and big-bucks divorces.

But there’s another side to their fabled love story, according to the upcoming blockbuster Paul Newman: A Life by Shawn Levy.

The blockbuster bio claims Newman – who died of cancer Sept. 26 at age 83 – began a year-long affair with divorced Hollywood journalist Nancy Bacon during the filming of Butch Cassidy and the Sundance Kid in 1969.

What’s more, the book charges that Newman’s co-star Robert Redford helped hide the affair.

Newman’s former mistress told The ENQUIRER she has no regrets about the story being told less than a year after the star’s passing.

"As long as it’s truthful, why not?" says Bacon. "That was the wild ’60s!"

The book details how Joanne was back in Connecticut raising the couple’s children when the blistering affair erupted and caused a brief secret separation between her and Paul after 11 years of marriage.

"On a magazine assignment, Nancy had traveled to the Butch Cassidy set in Mexico, and Paul fell for her quickly!"

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